1. Field of the Invention
The present invention is related to a communication apparatus, and more particularly to a communication apparatus for recognizing an ID packet comprised in an RF signal.
2. Description of the Related Art
Bluetooth wireless technology is a short-range communications technology, which is able to replace cables which connect portable and/or fixed devices for communications while maintaining high levels of security. The key features of Bluetooth technology are robustness, low power, and low cost. The Bluetooth specification defines a uniform structure for a wide range of devices to connect and communicate with each other.
All Bluetooth devices default to a standby mode. In a standby mode, unconnected devices periodically listen for messages. This procedure is called scanning which is divided into two types: page scan and inquiry scan. A page scan is defined as a connection sub-state in which a device listens for its own device access code (DAC) (via a “page”) for a scan window duration (11.25 ms) every 1.28 seconds in order to set up an actual connection between devices. An inquiry scan is very similar to a page scan except that in this sub-state the receiving device scans for the inquiry access code (IAC) (via an “inquiry”). The inquiry scan is used to discover which devices are in a range and addresses and clocks of devices in the range. Therefore, a normal scan procedure is typically performed during the scan window (11.25 ms) for a Bluetooth device.
A page sub-state is used by a master Bluetooth device to activate and connect to a slave Bluetooth device which periodically wakes up in the page scan sub-state. The master Bluetooth device tries to capture the slave Bluetooth device by repeatedly transmitting the slave's device access code (DAC) in different hop channels. In the page sub-state, the master Bluetooth device transmits the device access code (ID packet) corresponding to the targeted slave Bluetooth device for connection, rapidly on a large number of different hop frequencies. Since the ID packet is a very short packet, the hop rate can be increased from 1600 hops/s to 3200 hops/s. Since the Bluetooth clocks of the master and the slave Bluetooth devices may not be synchronized, in this case, the master Bluetooth device would not precisely know when the slave Bluetooth device has waken up and which hop frequency the slave Bluetooth device is on. Therefore, the master Bluetooth device transmits a train of identical DACs at different hop frequencies, and listens in between the transmitted intervals until the master Bluetooth device receives a response from the slave Bluetooth device. FIG. 1 shows a timing diagram illustrating page and inquiry scan transmissions, wherein pairs of page or inquiry scan messages 100 are repeated within the scan window (11.25 ms) in accordance with the Bluetooth specification.
However, when in standby mode, a Bluetooth device will consume power due to the inquiry scan and the page scan. This can be undesirable in that considerable battery power is consumed even while the Bluetooth device is unconnected.
Therefore, a communication apparatus and a Bluetooth ID packet recognition method thereof are desired to reduce power consumption of the communication apparatus when in a standby mode.